1. Field of the Invention
The present invention relates to a device for recording and/or reproducing digital data having a plurality of kinds of rates, and a method for reproducing the same.
2. Description of the Related Art
In recent years, various kinds of digital video cassette recorders (hereinafter, referred to as DVCRs) for recording video signals such as TV signals in digital form have been developed. However, since video signals contain a great amount of information, in the case where the video signals are recorded in digital form in a storage medium such as a tape, a long recording time is required. In view of such a problem, a method for recording video signals, which are subjected to high efficiency coding, in digital form has been proposed, for example in the International Conference on Consumer Electronics (ICCE) Jun. 6-9, 1989, Digest of Technical Papers WPM8.6 xe2x80x9cAN EXPERIMENTAL STUDY ON A HOME-USE DIGITAL VTRxe2x80x9d.
In the past, DVCRs record input video signals in synchronization with a field frequency thereof. More specifically, a magnetic head mounted in a rotary cylinder rotating in synchronization with the field frequency records video signals in tracks each having a track angle predetermined in accordance with set standards.
DVCRs use a rotary cylinder for the purpose of enhancing a recording density, and record data in tracks so as to be disposed on a magnetic tape in the diagonal direction of a magnetic tape traveling direction. For example, when a magnetic tape is wrapped around a rotary cylinder provided with two magnetic heads by about 180 degrees and the rotary cylinder rotates at a speed of 9000 rpm (rotation per minute), 18000 tracks are recorded on the magnetic tape per minute.
In general, DVCRs reproduce data in the same state as in the recorded state, except for special reproduction such as scene search, still, and slow reproductions. If data is reproduced in the state different from the recorded state, normal reproduction cannot be obtained. Thus, in the case of producing DVCRs, mechanical design specifications such as a track angle and a tape traveling speed should be strictly observed.
Since there are various kinds of high efficiency coding, the data rate after being subjected to high efficiency coding takes various values. Particularly in pre-recorded soft tapes, etc., the data rate is required to be decreased by high efficiency coding for the purpose of reducing tape cost.
In recent years, studies to supply digital video signals at a very low data rate in video services utilizing a digital TV broadcasting, a CATV, a telephone, etc. have been made. For example, the data rate of DVCRs for broadcasting is very high, i.e., 270 Mbit/s; however, a method for transmitting data after decreasing the data rate to 3 to 12 Mbit/s by filtering, high efficiency coding, etc. and a method for recording data after decreasing the data rate to 25 Mbit/s have been put into practical use. Furthermore, regarding TV signals, in addition to the NTSC system and the PAL system, 1125 line-60 field system and 1250 line-50 field system have been put into practical use.
In the case where a plurality of data rates are obtained depending upon TV signal systems or high efficiency coding methods after coding, a recording method and a reproducing method suitable for each data rate are required.
In general, the recording density and track pitch of the magnetic tape are respectively kept at nearly predetermined levels. Thus, the number of tracks and the tape traveling speed per predetermined period of time are increased in proportion to the data rate. When data is recorded at a data rate different from a normal recording data rate, a signal processing circuit and a device having a completely different cylinder construction are required. It is desired that data in one tape is copied to another tape for a short period of time. In particular, when a great amount of pre-recorded soft tapes, etc. are produced, it is desired to copy data at a data rate higher than normal for a short period of time so as to shorten the time for producing the tapes.
The method for recording digital data of the present invention by using a recording device recording a data stream having a predetermined data rate of n bit/s (n is a positive number) on a recording medium, comprises the steps of:
performing a data conversion step by receiving a plurality of input data streams having total data rates of n bit/s or less and converting the plurality of input data streams into a single output data stream having a data rate of n bit/s or less; and
performing a data recording step by recording the single output data stream.
Alternatively, the method for recording digital data of the present invention by using a recording device recording a data stream having a predetermined data rate of n bit/s (n is a positive number) on a recording medium, comprises the steps of:
performing a data conversion step by receiving a single input data stream having a data rate of n/i1 bit/s (n is a positive number, and i1 is an integer of 2 or more) and converting the single input data stream into a single output data stream having a data rate of n bit/s or less; and
performing a data recording step by recording the single output data stream for i1 times.
In one embodiment of the present invention, the plurality of input data streams include i2 data streams each having a data rate of n/i2 bit/s (n is a positive number, and i2 is an integer of 2 or more) or less.
In another embodiment of the present invention, the data conversion step includes the step of receiving i3 input data streams each having a data rate of n/i3/i4 bit/s (n is a positive number, and i3 and i4 are integers of 2 or more) and converting the plurality of input data streams into the single output data stream having a data rate of n/i4 bit/s, and
the data recording step includes the step of recording the single output data stream for i4 times.
In still another embodiment of the present invention, the data recording step includes the step of recording digital data indicating the number of the input data streams on the recording medium.
In still another embodiment of the present invention, the data recording step includes the step of recording digital data indicating the number of the input data streams on an auxiliary storage medium provided in a cassette accommodating the recording medium.
In still another embodiment of the present invention, the data recording step includes the step of recording digital data indicating the number of the input data streams and the number of repetition of recording on the recording medium.
In still another embodiment of the present invention, the data recording step includes the step of recording digital data indicating the number of the input data streams and the number of repetition of recording on an auxiliary storage medium provided in a cassette accommodating the recording medium.
Alternatively, the method for recording digital data of the present invention by using a recording device having a head mounted on a rotary cylinder, the recording device recording a data stream having a predetermined data rate of n bit/s (n is a positive number) on a traveling recording medium, comprises the steps of:
performing a data recording step by receiving an input data stream having a data rate of n/j bit/s or less (j is an integer of 2 or more), setting a traveling speed of the recording medium to be 1/j of a stand ard traveling speed and recording the output data stream on the recording medium by 1/j of scan times of the recording medium by the head.
In one embodiment of the present invention, the recording device includes paired heads, the paired heads are respectively provided so as to be symmetric with respect to a rotation axis of the rotary cylinder and have different azimuths, the recording device records the output data stream by helically scanning the recording medium, and the j is an odd number.
In another embodiment of the present invention, the data recording step includes the step of recording digital data indicating a value of the j on the recording medium.
In still another embodiment of the present invention, the data recording step includes the step of recording digital data indicating a value of the j on an auxiliary storage medium provided in a cassette accommodating the recording medium.
In still another embodiment of the present invention, the data recording step includes the step of recording digital data indicating a value of the j on the recording medium.
In still another embodiment of the present invention, the data recording step includes the step of recording digital data indicating a value of the j on an auxiliary storage medium provided in a cassette accommodating the recording medium.
Alternatively, the method for recording digital data of the present invention by using a recording device recording a data stream having a predetermined data rate of n bit/s (n is a positive number) on a recording medium, comprises the step of:
performing a data recording step by receiving a data stream having a data rate of nxc3x97(k1/k2) bit/s (k1, and k2 are integers of 2 or more, and k1 less than k2), setting a traveling speed of the recording medium to be k1/k2 times, and recording the data stream on the recording medium.
In one embodiment of the present invention, the data recording step includes the step of recording digital data indicating a value of the k1/k2 on the recording medium.
In another embodiment of the present invention, the data recording step includes the step of recording digital data indicating a value of the k1/k2 on an auxiliary storage medium provided in a cassette accommodating the recording medium.
According to another aspect of the present invention, the digital data recording device provided with a rotary cylinder, and a head mounted on the rotary cylinder, for recording digital data on a recording medium, comprises
recording means for recording a data stream having a predetermined data rate on the recording medium based on a recording format capable of selecting a plurality of track angles determined in accordance with a speed vector of the head and a speed vector of the recording medium.
In one embodiment of the present invention, the above-mentioned digital data recording device comprises first recording control means for controlling traveling of the recording medium so that the data stream is recorded on the recording medium once in every m times scans of the head when the data stream has a data rate which is 1/m (m is a natural number) of a predetermined data rate.
In another embodiment of the present invention, the above-mentioned digital data recording device comprises second recording control means for stopping traveling of the recording medium so as not to record the digital data on the recording medium for a predetermined period of time.
In still another embodiment of the present invention, the above-mentioned digital data recording device comprises second recording control means for stopping traveling of the recording medium so as not to record the digital data on the recording medium for a predetermined period of time.
Alternatively, the digital data recording device of the present invention for recording a data stream having a predetermined data rate of n bit/s (n is a positive number), comprises:
data compressing means for receiving an input data stream having a data rate of n bit/s or less and performing time axis compression with respect to the input data stream so that the input data stream is compressed into an output data stream having a data rate of n bit/s; and
data recording means for recording the output data stream on the recording medium.
Alternatively, the digital data recording device of the present invention provided with a rotary cylinder, and a head mounted on the rotary cylinder, for recording digital data on a recording medium, comprises
recording means for recording a data stream at a track pitch smaller than a track pitch at which normal-rate signals are to be recorded, in a case where the data stream is low-rate signals to be reproduced at a data rate lower than a predetermined data rate.
In one embodiment of the present invention, the recording means records digital data indicating at least one of the group consisting of a track angle during recording, a traveling speed of the recording medium, a rotation number of the rotary cylinder, and a track pitch of the recording medium.
In another embodiment of the present invention, the recording means records digital data indicating at least one of the group consisting of a track angle during recording, a traveling speed of the recording medium, a rotation number of the rotary cylinder, and a track pitch of the recording medium.
According to still another aspect of the present invention, the digital data reproducing device for reproducing digital data from a recording medium by using a head mounted on a rotary cylinder, comprises:
data reproducing means for reproducing digital data recorded on the recording medium at a data rate higher than a data rate during recording by increasing a rotation number of the rotary cylinder; and
data output means for selectively outputting required data among the reproduced digital data.
Alternatively, the digital data reproducing device of the present invention for reproducing digital data from a recording medium by using a head mounted on a rotary cylinder, comprises:
data reproducing means for reproducing low-rate signals, which are to be reproduced at a data rate lower than a predetermined data rate, at a data rate higher than a data rate of the low-rate signals with the rotation number of the rotary cylinder substantially equal to the rotation number of the rotary cylinder during reproducing normal-rate signals which are to be reproduced at the predetermined data rate, in a case where the low-rate signals and the normal-rate signals are present; and
data output means for selectively outputting required data among the reproduced digital data.
In one embodiment of the present invention, the data reproducing means and the data output means reproduce the low-rate signals by using a processing method utilized for slow reproduction of the normal-rate signals.
In another embodiment of the present invention, the data rate is in proportion with a traveling speed of the recording medium.
In still another embodiment of the present invention, the data rate is in proportion with a traveling speed of the recording medium.
According to still another aspect of the present invention, the digital data recording and reproducing device comprises recording means for recording a data stream having a predetermined data rate on a recording medium by using a head mounted on a rotary cylinder and reproducing means for reproducing a data stream recorded by the recording means,
wherein, in a case where a data stream to be recorded is a data stream having a low data rate to be reproduced at a data rate lower than a predetermined data rate, the reproducing means reproduces the data stream at the predetermined data rate, and the recording means records the data stream reproduced by the reproducing means at the predetermined data rate.
In one embodiment of the present invention, the data rate is in proportion with a traveling speed of the recording medium.
In another embodiment of the present invention, the recording means records digital data indicating at least one of the group consisting of a track angle during recording, a traveling speed of the recording medium, a rotation number of the rotary cylinder, and a track pitch of the recording medium.
Alternatively, the digital data recording device of the present invention provided with a rotary cylinder, and a head mounted on the rotary cylinder, for recording digital data on a recording medium, comprises
recording means for recording the digital data on the recording medium so that an angle of tracks formed on the recording medium traveling at a recording medium traveling speed different from a predetermined recording medium traveling speed is equal to an angle of tracks formed on the recording medium traveling at the predetermined recording medium traveling speed.
In one embodiment of the present invention, the recording means controls an angle formed by a rotation axis of the rotary cylinder and a traveling direction of the recording medium in accordance with the recording medium traveling speed.
In another embodiment of the present invention, the recording means includes head moving means for moving the head in a direction parallel with a rotation axis of the rotary cylinder.
In still another embodiment of the present invention, the recording means records data indicating the recording medium traveling speed on the recording medium.
Thus, the invention described herein makes possible the advantages of (1) providing a recording device in which long-time recording can be performed by converting a format; (2) providing a recording and reproducing device in which data having a data rate of a plurality of input data streams can be recording and reproduced; (3) providing a recording device in which the rotation number of the cylinder and the tape traveling speed during recording can be set at various kinds of values by using a recording format capable of selecting a plurality of types of track angles; (4) providing a reproducing device in which all the data can be reproduced even in the case where the recording track angles are not identical; (5) providing a recording device in which low-rate signals are subjected to a time axis compression in order to be recorded in a short period of time at a normal data rate; (6) providing a recording device in which data can be recorded with a track pitch smaller than standardized one; (7) providing a recording and reproducing device in which data is reproduced at a data rate higher than the data rate which is to be used for reproducing and the reproduced data is recorded at the higher data rate, making it possible for high-speed copying; and (8) providing a recording device in which even data having a data rate other than a standard one can be appropriately recorded.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.